International maritime agreements require that most new oil tankers have to be fitted with a system capable of keeping the cargo oil and ballast water, including their residues, physically apart at all times, i.e. a segregated ballast system must be fitted.
The inventor's U.S. Pat. No. 4,117,796 "Double Sectioned Tank" discloses a means whereby segregation of the cargo oil and ballast water is achieved without most of the very substantial loss of cargo carrying capacity necessitated by the standard method of using entirely separate tanks to contain each of the two substances.
The present invention relates generally to improvements to the aforesaid U.S. Patent. The improvements make unnecessary certain items in the patent and will facilitate the manufacture, installation, operation, and maintenance of the diaphragms disclosed in the patent, while also providing means whereby the hull girder strength may be improved. The provision of ballast tanks located low down in a tanker fitted with the improvements may also increase seakeeping and ship stability performance by reducing stiffness in the cargo loaded condition.
It will be noted that a standard segregated ballast oil tanker will have to designate capacity equivalent to approximately one-third of it's cargo capacity to the carriage of segregated ballast. In the cargo loaded condition this space will be filed with air, i.e. the tanker will carry only approximately two-thirds of the cargo it would be capable of carrying if it were an ordinary non-segregated ballast tanker.
A segregated ballast tanker that is fitted with the present invention will utilize a large proportion of the designated ballast space to carry revenue generating cargo.